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Last night's broadcast of the CBS Evening News with Katie Couricended with a segment on the struggling recovery of the California sea otter (Enhydra lutris nereis), a species federally listed as threatened.

Mortality from sharks and heart disease are just a fraction of the many natural and human factors that Tim Tinker and colleagues are studying to understand the slow recovery of California sea otter populations.

WERC lead scientist Tim Tinker is collaborating with scientists in the U.S. and Canada to uncover clues to sea otter population health. (Image courtesy of CBS News)

The scientists are looking at clues including polluted runoff from inland cities, parasites, toxic algal blooms, climate change, food availability and even sea otter genes to solve the mystery. Whatever they discover about the factors impacting sea otter recovery also will shed light on the factors that impact the rest of our nearshore ecosystem -- including our water quality and fisheries.

As for the increased shark attacks, they are so far a uniquely Californian phenomenon and a puzzling one at that. As CBS reported, white sharks (Carcharodon carcharias) do not eat the sea otters they bite. Researchers have one hypothesis involving the recovering populations of seals and sea lions -- which are known prey of white sharks.

As seal and sea lion breeding colonies grow, sea otters who wander into those waters might become collateral damage. Sea otters are the same size and shape as juvenile seals and sea lions, but without the nutritious blubber that sharks prefer. But one mistaken bite from a confused shark still leaves the otter mortally wounded.

It's complex scenarios and trends like these that USGS biologists are trying to understand and explore. The research continues.